Their faces come in hues from orange to blue and their facial hair ranges from
bushy white beard to neat ginger moustache. Now scientists have concluded
that guenon monkeys evolved their remarkable facial patterns to prevent
interbreeding.

Multiple species of guenons live side-by-side in the forests of Central and
West Africa, often travelling, feeding and sleeping in groups, creating a
high risk of breeding across species.

The monkeys, which are roughly the size of cats, are already known to have
chirps, sneezes and whistles that are distinct to each species. The latest
findings suggest their markings, which include coloured eyebrow